How this works
This is a heuristic, not a formula — actual Yocto disk usage depends heavily on which layers you include, image size (core-image-minimal vs a full graphical image), number of BSPs, and whether you clean between builds. As a starting point: a single full build (downloads + sstate + tmp/work) commonly lands in the 40-80GB range, and DL_DIR/SSTATE_DIR shared across machine configs (recommended in local.conf) avoids re-downloading and re-building common components per target. Always leave meaningful headroom beyond this estimate — a full disk mid-build is one of the most common CI failures in Yocto pipelines.